Patent GB-880076-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: HOPLEY HORACE EDWARD
IPC: H04Q3/00
Filed: 1959-08-22
Abstract: 880,076. Automatic-exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd July 28, 1960 [Aug. 22, 1959], No. 28763/59. Class 40 (4). In a system in which final selectors are normally arranged for calling party release and in which an interception circuit giving access to an operator may be interposed between the final selector multiple and the line of a subscriber liable to receive malicious calls, a signal returned from the interception circuit enables the final selector to be held from the called end and, if the call involves a junction, causes a similar signal to be returned to the outgoing relay-set so that the connection is maintained and the call can be traced. Final selector, Figs. 4, 5.-At the end of the first digit received, change-over relay E energizes, followed by relay G which allows wiperswitching relay WS to operate if required. At the end of the second digit relay E falls back and connects test relay 4 in series with G to test wiper P1, or P2. If the wanted line is busy G holds and gives a busy signal. If the wanted line is idle G falls back and earths relay H, thus permitting its operation. Relay J connects up ringing current, and upon reply ring-trip relay F, back-bridge relay D and relay E pull up in turn and metering takes place. When the calling party hangs up, the relapse of line relay A normally short-circuits guard relay B and the connection is released. But if the called party is one whose calls are being intercepted, after the operation of H, relay (upper winding) re-energizes to positive battery on the + wiper and makes the short-circuiting of B dependent on the release of D when the called party or the interception operator clears. Moreover, relay G connects positive battery to the incoming - wire during the release time of J, so that, if the call has come in over a junction, a relay is operated in the outgoing relay-set, Figs. 2, 3 (not shown), thus causing the junction to be held from the called end. This relay also repeats the holding signal in the backward direction in case the relay-set is situated at a tandem exchange. Interception circuit, Fig. 1.-This is interposed when required between the subscriber's line circuit LC and the final selector multiple FSM, plug P being inserted in the subscriber's jack PJ on the main distributing frame MDF. On an incoming call, positive battery through relay IG is applied to the + wire of the final selector to operate relay G, and when ringing is applied the ring return battery is effective to operate IG. Relay GH pulls up and extends the ringing current to the subscriber's line SL, the return battery being provided over resistor R7. Upon reply, ring-trip relay F releases IG and the called line is connected to feed relay IA, which pulls up followed by IB, ICD, the latter closing a loop for back-bridge relay D in the final selector. If the call is a malicious one, the subscriber can signal the operator by dialling any digit, e.g. 0, whereupon an indication is given over wire OPC. The operator enters the connection and at the same time holds IB over wire OPH. The loop holding relay D in the final selector is thus maintained, and the call can be traced if it is considered necessary.